Wouldn’t this have been easier to post in post #2?
So you are going to swap your hood to go to the track? Why not just run no filter then? And if its only for the track, then why do you care about the color? I’m assuming you’ll have DRs or something similar mounted on some probably ugly but light weight rims with a fairly stripped interior, so I’m not seeing how the color became the gating item in this project?
That said, if your filter is directly against the front of the hood as you describe, it will be nearly impossible to create something to keep the rain out that won’t keep the air out too. “Ram air” systems in factory cars use various louvers and bends in the systems to make sure that there is a place for water to escape, and with the filter right against the surface of the hood, you won’t have space for that.
That said, is the gain you are going to get from this, worth the effort and cost? It seems to me like the time and money could be spent somewhere else that would yield more, if you were super lucky, I wouldn’t expect more than a few HP max (as in less than 5).